The history of the law of neutrality is a dynamic one. Never has there been an area of law that has undulated to the whim of state interest and contended with the extreme demarcation between belligerency and non-belligerency in the way that neutrality has. The struggles of neutrality over the centuries, particularly as an important contributor to the history of international law, have remained largely neglected within academic scholarship. Few authors have embarked on a qualitative treatment of neutrality in its own right. This is understandable, given its contention with the more dominant contexts of war and peace. Dr. Maartje Abbenhuis, however, adds to the small number of academics that have focused on this topic.

Abbenhuis’ admirable work on ‘An Age of Neutrals’ follows the life of neutrality in the ‘long’ nineteenth century (p. 16), highlighting the quite apparent disparity between its active role and function between 1815 and 1914 as opposed to its virtually redundant and rather different position in today's world. This is not a comprehensive history, as Abbenhuis herself points out early on in the book, but instead exposes the reader to new and different angles from which to view European political and economic powerplay during this dynamic historical period. Neutrality was crucial for all players in the game of war and peace – for belligerent and non-belligerent alike – and contributed massively to the development of international law and the stabilization of the European balance of powers. Whilst all of these insights are valuable for scholarly work into European (and international) history, quite how influential neutrality was for both international law and diplomacy in the pre-1914 era is perhaps the most obvious strength of Abbenhuis’ book. Prudently, Abbenhuis posits neutrality as an indispensable tool for all manner of states in foreign policy. It not only reinforced the foundations of the Congress system, but restricted the use of force in the nineteenth century; enhancing global commercial and imperial power, especially for Great Britain, but also the profiles of neutral countries. Essentially, the book delves into the true impact of neutrality, which is often understated or even ignored.

Following the Napoleonic Wars, the Congress of Vienna gave rise to the importance of neutrality for European diplomacy. To avoid future conflicts similar to the one that had come to an end, but to facilitate peaceful and harmonious international relations between states. Neutrality, in this sense, allowed the great states to continue with their realpolitik agenda whilst simultaneously hindering them in how to pursue it as such. In order to manage European affairs there needed to be a system that was agreed and adhered to by all states. Neutrality was a means in which to ground international dispute resolution within the congress system, distinguishing itself from previous forms. Placing neutrality centre-court within the Congress, the author explains that neutrality was a useful dispute resolution tool that limited the negotiating leeway amongst states pursuing war or likely to pursue war.

The book also highlights the ‘self-serving’ nature of neutrality, which was eventually no more appreciated than the super power Great Britain (p. 239). The British Government recognized the benefits of refraining from war with the other great powers, especially through the realization that belligerency may threaten the very core of the global empire that they had fought so hard to build. It was after 1856 that Britain truly understood the value of neutrality, which would allow them to protect and enhance their commercial and imperial interests around the entire globe. With this, the Declaration of Paris was signed, upon which Britain ‘promoted and adopted a new set of international rules of economic warfare’ and ‘overturned not only the Rule of 1756 but also the long-defended idea that Britain should jealously guard its rights to control the seas by aggressive naval means’ (p. 87). Whilst over 40 countries signed the Declaration, it is indeed Britain that left its footprint and ‘determined the neutral freedoms offered by the Declaration of Paris’ (p. 88). Neutrality admitted states into a global economy in times of war and peace. The desire of the great powers to achieve this was best reflected in the evolution of maritime neutral rights and later crystallized in The Hague Peace Conferences of 1899 and 1907 and the 1909 London Declaration.

The book quite rightly emphasizes neutrality's place in the development of international law. It, however, also accurately highlights the law's interconnection with cultural and political aspects of neutrality's growth in the long ‘janus-faced’ nineteenth century, battling growing state rivalry on the one hand, yet as Abbenhuis puts it, ‘the golden age of peace activism and international law’ on the other (pp. 147–148). Arbitration then became an important and popular method by which to resolve disputes peacefully. The proliferation of arbitration treaties following the turn of the century, and after the famous Alabama case, illustrates its popularity well. But neutrality had a large part to play in the way the international system of ‘power, pragmatism and idealism’ was developing. Abbenhuis rightly points out its function in maintaining state power play, to the facilitation of peace and consequently, within the discussions on and practices of arbitration. It was ‘as much a culturally constructed idea, promoted and debated by a variety of interested parties and the educated reading public at large, as it was a principle of international relations and international law’ (p. 148).

An Age of Neutrals is an impressive investigation into the political practice of what was a quite crucial concept in a remarkably complex and fascinating era. It should be mentioned, however, that although the book is aptly sub-titled Great Power Politics, Abbenhuis clearly affirms that neutrality was fundamentally a ‘legal term’, ‘recognised first and foremost by its legal definition’ and a cornerstone in the development of international law (p. 238). One would therefore infer a greater emphasis on substantive legal content than what is actually assessed in the book. Sources such as that of Lassa Oppenheim's International Law Treatises or other standard commentaries on the law of nations were certainly included in the analysis, but at a very minimal level. The nineteenth century (and earlier) provides us with an array of relevant legal sources and doctrinal writings on neutrality that, if utilized, would have substantially enhanced the quality of the book in terms of the legal value of neutrality, even if Great Power Politics were indeed the focus. In the same way, a more in-depth analysis of the influence and interrelations of legal doctrine, but also non-state actors such as peace activists, on state decision-making, would have done no harm.

Abbenhuis concludes that ‘in the war of 1914–1918, most, although not all, of the systematic applications of neutrality that had existed in the previous century collapsed under the excessive pressure put on them by the great-power belligerents’ (p. 242). This is briefly explained and later followed by the further assertion that ‘nineteenth-century neutrality had an important after-life in the post-war era, particularly as a cultural, humanitarian, scientific and internationalist ideal’ (p. 243). Abbenhuis should have paid more attention to at least the demise of neutrality. As it stands, the transition to the end of neutrality upon the arrival of the Great War is surprisingly short and in need of elaboration. Nonetheless, these points, including neutrality's post-war ‘after-life’, spark a curiosity for more research into this area. The book provides an opportunity for additional scholarship in this field and a solid basis on which to work. The insight Abbenhuis brings to neutrality should trigger further research, especially since Abbenhuis herself admits that ‘the connections that existed among the cultural elements of nineteenth-century neutrality and its twentieth century counterparts were essential and deserve much more research and attention’ (p. 243). Despite these slight weaknesses, it is hard to dismiss this well-written and extremely informative piece of work. Abbenhuis, without a doubt, makes a significant contribution to the much-neglected neutrality as much more than a mere concept. The book is therefore interesting not only for historians and political scientists, but also international lawyers.